[CentOS] [Fwd: Server is overloaded, any tips?]

Yesterday our website was acting a little odd, and i received a few email complaints. Running 'top' showed that we had a very high load average, today the load average is even higher!

load average: 13.18, 12.49, 10.48

It is pretty unlikely that our site grew in popularity that quickly, and taking a look at the log file it was saying that a certain directory was not found, when in fact it was just a mod-re-write rule and was not supposed to exist. The website works fine... i am stumped and the error log is getting quite big! Does anyone have any tips on how to find the problem and address it accordingly (quickly)? Many thanks